1. Field of the Invention
The present invention relates to a lighting device for display devices, a liquid crystal display device, and a light source lamp. More specifically, the present invention relates to a lighting device for display devices, which is preferably used as a backlight of a transmissive or transflective liquid crystal display device having a transmissive region in a liquid crystal display element. The present invention also relates to a liquid crystal display device including such a lighting device for display devices, and a light source lamp.
2. Description of the Related Art
Lighting devices for display devices are devices for lighting a device having a display that uses light, and have been widely used in backlight parts in liquid crystal display devices, for example. That is, a transmissive or transflective liquid crystal display device generally includes a lighting device for display devices in a backlight part for causing light to enter a liquid crystal panel because liquid crystal panels themselves do not emit light in the liquid crystal display devices. Such liquid crystal display devices are essential for displaying information or image. Products with high quality, fully taking advantage of characteristics of liquid crystal displays, that is, low electric power consumption, lightweight, slim profile, have been recently used in display panels such as monitors for consumer displays, monitors for industrial equipment, and Personal Digital Assistants. In addition, the field of application of such liquid crystal display devices is becoming more and more widespread.
There are currently two types of back lights used in liquid crystal display devices: an edge light type (side light type) and a direct type. In the edge light type, a bar-shaped light source 72 such as cold cathode fluorescent tube is held in a frame 73 and disposed on the side of a transparent plate 71 called a light guide plate, as shown in FIG. 8. In this case, light is made to enter the light guide plate 71 from the light source, and outputted from the inside of the light guide plate 71 through the optical sheet 74 to the liquid crystal panel 75 side by one of a frosting process, printing, prism treatment, or the like. As a result, the liquid crystal display device can be made thinner, but an increase in the light source for increasing brightness directly affects the thickness of a module. The so-called light guide plate 71 gets heavier in a large size of 20 inches or more because a heavy continuum such as acrylic continuum is used.
In the direct type, a plurality of bar-shaped light sources 83, such as cold cathode fluorescent tubes, is provided on the back side of a display element 87 such as a liquid crystal panel, as shown in FIG. 9. In this case, light from the bar-shaped light source 83 is caused to almost directly enter the display element 87. A diffusing plate 85 is often provided between the display element 87 and the light source 83 for eliminating an image of the bar-shaped light source 83. As a result, the direct type backlight has the following advantages: many light sources 83 can be provided; a light amount can be increased; loss of light is small because light is caused to enter the display element 87 directly; and increase in size greater than 20 inches can easily be achieved. However, the number of the light sources 83 increases and thereby the number of components increases. Thereby, the driving circuit of the light source 83 becomes larger. Furthermore, the electric power consumption also increases, and the total amount of heating becomes larger.
Such liquid crystal display devices began to advance in small display elements, and have been widely used as displays for laptop PCs or cellular phones. Thus, the technique has been developed. In these fields, a display size up to about 15 inches is a mainstream size, and reduction in thickness is a required condition. An edge light type has been selected in terms of merchantability. Such liquid crystal display devices currently have become dramatically larger because of completion of a process using a larger mother glass, and thereby have established a position as a household television (20 to 50 inches, for example) For such TVs, brightness is a more important basic performance characteristic than required for PCs or cellular phones. For example, a PC monitor generally has about 250 cd/m2 of specification value, but a brightness specification of 500 cd/m2 or more is needed for TVs. Because of such requirements, a direct type backlight is preferable for providing a large backlight with high brightness.
As conventional lighting devices for display devices, disclosed is a lighting device in which, in a liquid crystal display device using a direct type backlight, a frame side wall in the direction intersecting with a backlight (linear light source) or a frame between the linear light sources is sloped, and thereby reduction in brightness at both end edges of the linear light source is compensated to light a liquid crystal panel with uniform brightness distribution (for example, refer to Japanese Kokai Publication Hei-11-84377, pages 1 to 2). Also disclosed is a lighting structure of a liquid crystal TV in which a U-shaped, S-shaped, or M-shaped fluorescent tube is disposed on the back side of a liquid crystal panel (for example, refer to Japanese Kokai Publication Sho-62-102226, pages 1 to 4).
However, such devices have room for improvement in order to properly correspond to a liquid crystal field and the like, which requires high quality, increased size, and low cost for improvement in merchantability. In addition, such lighting devices have room for improvement, in their structural characteristics, so as to provide advantages in the production thereof by reducing the number of components; to be effective in electric power consumption when applied to a liquid crystal display device; to have high quality and merchantability; and additionally to have improved these properties especially in development of a liquid crystal TV and the like.